Emergency medicine provides care to a vast number of patients each year. In 2005, 115.3 million people visited emergency departments (EDs).1 Although the number of people who visit an ED significantly increased from 96.5 million in 1995 to 115.3 in 2005, the number of ED facilities decreased from 4176 to 3795 in the same period.1 This created additional pressure on ED physicians to reduce patient throughput time and the potential for increased neglect of psychiatric disorders.

This article provides an overview of the prevalence of psychiatric comorbidity among patients who present to the ED and documents the relationship of psychiatric comorbidity to disposition decisions. In addition, the implications of the observed comorbidity rates and disposition decisions are discussed.

Epidemiology

In 2002, 43% of all hospitalizations originated in the ED—a 17% increase since 1997.2 Hospitalization costs consume one-third of the entire US health care budget and make hospitalization the single most costly component of the health care system.2 It is of considerable interest, from both economic and mental health perspectives, to determine how often ED patients with single and multiple psychiatric disorders are hospitalized. At present, little is known about the extent of psychiatric comorbidity (defined as 2 or more co-occurring psychiatric disorders) in patients who present to the ED.

Before assessing comorbidity rates, we summarize the psychiatric prevalence obtained in the National Comorbidity Survey Replication (NCS-R) study.3 The data show that the 12-month prevalence of any psychiatric disorder was 26%. Of the total number of patients identified with a psychiatric disorder, 55% had a diagnosis of 1 disorder; 22.3% had 2 diagnoses; and 23% had 3 diagnoses. Estimated prevalences for the 4 most frequently occurring disorders were anxiety disorders, 18.0%; mood disorders, 9.5%; impulse control disorders, 8.9%; and substance use disorders, 3.8%.3 Other researchers have reported 12-month substance use disorder rates to be as high as 9.35%.4

There are several reasons to expect rates of psychiatric disorders among ED patients to equal (or exceed) those reported in the NCS-R study:

• There is a concentration of the homeless, chronically ill, uninsured, and impoverished in ED populations.5-8

• A strong relationship has been found between poverty and mental illness.11-13

Low rates of psychiatric disorders might be expected if ED physicians focus primarily on presenting physical complaints because of time constraints and, perhaps, because of a lack of interest in psychiatric problems in this setting. In 2001, 6% of all ED visits were for mental health issues.14 This 6% rate is far lower than the 26% reported by the NCS-R studyand indicates that ED physicians are not consistently screening for mental health disorders.14

The deinstitutionalization of mental health patients and a shortage of community-based psychiatric services have been identified as major contributors to the increased visits to EDs by patients with psychiatric disorders over the past decade.15-17 Psychiatric patients require intensive ED staff resources and close supervision, and when inebriated, psychotic, or belligerent, these patients can disrupt the care provided to other patients.18 According to the recent American College of Emergency Physicians study, 62% of ED directors surveyed said that psychiatric patients in the EDs received no psychiatric services before hospital admission or transfer.19 Close to one-quarter of the ED directors (23%) surveyed indicated that they had no community psychiatric resources available for psychiatric patients; over half (59%) reported that there were no services available for persons with substance use disorders or dual diagnoses.

While there are many community-based studies of psychiatric comorbidity, few researchers have examined how psychiatric comorbidity influences the disposition of ED patients.20-22 This is surprising because, compared with patients with a single psychiatric diagnosis, patients with multiple psychiatric disorders often have more severe pathology, increased illness duration, reduced treatment responsiveness and adherence, greater functional impairment, higher suicide rates, and increased ED visits.23-26

In our literature review, we found only 1 study that explicitly examined how psychiatric comorbidity influenced hospitalization decisions. In that study, which used data from the 2004 National Hospital Ambulatory Medical Care Survey (NHAMCS), ED patients with psychiatric comorbidity had a 5-fold increase in hospitalization relative to patients without psychiatric comorbidity.27

What our analyses show

We analyzed data from NHAMCS for 3 consecutive years (2002 through 2004).28-30 There were 91,118 visits by patients 15 years and older. We created psychiatric categories (such as depression, psychosis, substance use disorders) to be compatible with those in DSM-IV. The weighting, strata, and cluster factors provided by NHAMCS were used to estimate pop-ulation parameters and associated standard errors.

Approximately 6% of all 91,118 patients received a diagnosis of at least 1 psychiatric disorder (95% confidence interval (CI), 6.1% - 6.7%). The 4 most frequently occurring psychiatric categories were:

• Substance use disorders (2.27%; 95% CI, 2.10% - 2.46%).

• Mood disorders (1.63%; 95% CI, 1.50% - 1.78%).

• Anxiety disorders (1.24%; 95% CI, 1.14% - 1.35%).

• Psychoses (1.20%; 95% CI, 1.09% - 1.32%).

Approximately 1.3% (95% CI, 1.13% - 1.39%) of all patients visiting the ED had at least 2 psychiatric disorders. This represented about 2.8 million psychiatric comorbidity patient visits during the 3 years. The hospitalization rate of patients with 2 or more psychiatric disorders (48.49%) was much greater than the hospitalization rate of patients with 1 or no psychiatric disorder.

We also compared the hospitalization rate of patients with only psychiatric comorbidities and no medical conditions with that of patients with only a medical condition. Far more patients with comorbidities who had no medical condition were hospitalized than were patients with medical diagnoses and no psychiatric diagnosis (52.1% vs 17.93%, respectively). The 4 most frequently occurring comorbidity pairs were:

It is sobering to realize that when studies are designed to assess the prevalence of specific mental disorders in patients who present to the ED, the rates of several specific mental disorders are higher than the total annual psychiatric rate found in the NHAMCS data. For example, studies that explicitly screened for depression found the depression rate among ED patients to be at least 20%.31,32 Part of the reason for the low rate of depression diagnoses (1.63%) in the NHAMCS data is that physicians infrequently screen for depressive symptoms.33